.TH SNMPD.CONF 5 "01 Jun 2009" VVERSIONINFO "Net-SNMP"
.SH NAME
snmpd.conf - configuration file for the Net-SNMP SNMP agent
.SH DESCRIPTION
The Net-SNMP agent uses one or more configuration files
to control its operation and the management information
provided.
These files (\fBsnmpd.conf\fR and \fBsnmpd.local.conf\fR)
can be located in one of several locations, as described in the
.I snmp_config(5) 
manual page.
.PP
The (perl) application
.B snmpconf
can be used to generate configuration files for the
most common agent requirements.  See the
.I snmpconf(1)
manual page for more information, or try running the
command:
.RS
.IP "snmpconf -g basic_setup"
.RE
.PP
There are a large number of directives that can be specified,
but these mostly fall into four distinct categories:
.IP \(bu
those controlling who can access the agent
.IP \(bu
those configuring the information that is supplied by the agent
.IP \(bu
those controlling active monitoring of the local system
.IP \(bu
those concerned with extending the functionality of the agent.
.PP
Some directives don't fall naturally into any of these four
categories, but this covers the majority of the contents of
a typical
.B snmpd.conf
file.
A full list of recognised directives can be obtained by running
the command:
.RS
.IP "snmpd -H"
.RE
.SH AGENT BEHAVIOUR
Although most configuration directives are concerned with the MIB
information supplied by the agent, there are a handful of directives that
control the behaviour of \fIsnmpd\fR considered simply as a daemon
providing a network service.
.IP "agentaddress [<transport-specifier>:]<transport-address>[,...]"
defines a list of listening addresses, on which to receive incoming
SNMP requests.
See the section 
.B LISTENING ADDRESSES
in the
.I snmpd(8)
manual page for more information about the format of listening
addresses.
.IP
The default behaviour is to
listen on UDP port 161 on all IPv4 interfaces.
.IP "agentgroup {GROUP|#GID}"
changes to the specified group after opening the listening port(s).
This may refer to a group by name (GROUP), or a numeric group ID
starting with '#' (#GID).
.IP "agentuser {USER|#UID}"
changes to the specified user after opening the listening port(s).
This may refer to a user by name (USER), or a numeric user ID
starting with '#' (#UID).
.IP "leave_pidfile yes"
instructs the agent to not remove its pid file on shutdown. Equivalent to
specifying "-U" on the command line.
.IP "maxGetbulkRepeats NUM"
Sets the maximum number of responses allowed for a single variable in
a getbulk request.  Set to 0 to enable the default and set it to -1 to
enable unlimited.  Because memory is allocated ahead of time, sitting
this to unlimited is not considered safe if your user population can
not be trusted.  A repeat number greater than this will be truncated
to this value.
.IP
This is set by default to -1.
.IP "maxGetbulkResponses NUM"
Sets the maximum number of responses allowed for a getbulk request.
This is set by default to 100.  Set to 0 to enable the default and set
it to -1 to enable unlimited.  Because memory is allocated ahead of
time, sitting this to unlimited is not considered safe if your user
population can not be trusted.
.IP
In general, the total number of responses will not be allowed to
exceed the maxGetbulkResponses number and the total number returned
will be an integer multiple of the number of variables requested times
the calculated number of repeats allow to fit below this number.
.IP
Also not that processing of maxGetbulkRepeats is handled first.
.SS SNMPv3 Configuration
SNMPv3 requires an SNMP agent to define a unique "engine ID"
in order to respond to SNMPv3 requests.
This ID will normally be determined automatically, using two reasonably
non-predictable values - a (pseudo-)random number and the current
uptime in seconds. This is the recommended approach. However the
capacity exists to define the engineID in other ways:
.IP "engineID STRING"
specifies that the engineID should be built from the given text STRING.
.IP "engineIDType 1|2|3"
specifies that the engineID should be built from the IPv4 address (1),
IPv6 address (2) or MAC address (3).  Note that changing the IP address
(or switching the network interface card) may cause problems.
.IP "engineIDNic INTERFACE"
defines which interface to use when determining the MAC address.
If \fIengineIDType 3\fR is not specified, then this directive
has no effect.
.IP
The default is to use eth0.
.\"
.\" What if this doesn't exist ?
.\"
.SH ACCESS CONTROL
.B snmpd
supports the View-Based Access Control Model (VACM) as defined in RFC
2575, to control who can retrieve or update information.  To this end,
it recognizes various directives relating to access control.
These fall into four basic groups.
.SS SNMPv3 Users
.IP "createUser [-e ENGINEID] username (MD5|SHA) authpassphrase [DES|AES] [privpassphrase]"
.IP
MD5 and SHA are the authentication types to use.  DES and AES are the
privacy protocols to use.  If the privacy
passphrase is not specified, it is assumed to be the same as the
authentication passphrase.  Note that the users created will be
useless unless they are also added to the VACM access control tables
described above.
.IP
SHA authentication and DES/AES privacy require OpenSSL to be installed and
the agent to be built with OpenSSL support.  MD5 authentication may be
used without OpenSSL.
.IP
Warning: the minimum pass phrase length is 8 characters.
.IP
SNMPv3 users can be created at runtime using the
.I snmpusm(1)
command.
.IP
Instead of figuring out how to use this directive and where to put it
(see below), just run "net-snmp-config --create-snmpv3-user" instead,
which will add one of these lines to the right place.
.IP
This directive should be placed into the
PERSISTENT_DIRECTORY/snmpd.conf file instead of the other normal
locations.  The reason is that the information is read from the file
and then the line is removed (eliminating the storage of the master
password for that user) and replaced with the key that is derived from
it.  This key is a localized key, so that if it is stolen it can not
be used to access other agents.  If the password is stolen, however,
it can be.
.IP
If you need to localize the user to a particular EngineID (this is
useful mostly in the similar snmptrapd.conf file), you can use the -e
argument to specify an EngineID as a hex value (EG, "0x01020304").
.IP
If you want to generate either your master or localized keys directly,
replace the given password with a hexstring (preceeded by a "0x") and
precede the hex string by a -m or -l token (respectively).  EGs:
.IP
.RS
.nf
[these keys are *not* secure but are easy to visually parse for
counting purposes.  Please generate random keys instead of using
these examples]

createUser myuser SHA -l 0x0001020304050607080900010203040506070809 AES -l 0x00010203040506070809000102030405
createUser myuser SHA -m 0x0001020304050607080900010203040506070809 AES -m 0x0001020304050607080900010203040506070809
.fi
.RE
.IP
Due to the way localization happens, localized privacy keys are
expected to be the length needed by the algorithm (128 bits for all
supported algorithms).  Master encryption keys, though, need to be the
length required by the authentication algorithm not the length
required by the encrypting algorithm (MD5: 16 bytes, SHA: 20 bytes).
.SS Traditional Access Control
Most simple access control requirements can be specified using the
directives \fIrouser\fR/\fIrwuser\fR (for SNMPv3) or
\fIrocommunity\fR/\fIrwcommunity\fR (for SNMPv1 or SNMPv2c).
.IP "rouser USER [noauth|auth|priv [OID | -V VIEW [CONTEXT]]]"
.IP "rwuser USER [noauth|auth|priv [OID | -V VIEW [CONTEXT]]]"
specify an SNMPv3 user that will be allowed read-only (GET and GETNEXT)
or read-write (GET, GETNEXT and SET) access respectively.
By default, this will provide access to the full OID tree for authenticated
(including encrypted) SNMPv3 requests, using the default context.
An alternative minimum security level can be specified using \fInoauth\fR
(to allow unauthenticated requests), or \fIpriv\fR (to enforce use of
encryption).  The OID field restricts access for that
user to the subtree rooted at the given OID, or the named view.
An optional context can also be specified, or "context*" to denote a context
prefix.  If no context field is specified (or the token "*" is used), the
directive will match all possible contexts.
.IP "rocommunity COMMUNITY [SOURCE [OID | -V VIEW [CONTEXT]]]"
.IP "rwcommunity COMMUNITY [SOURCE [OID | -V VIEW [CONTEXT]]]"
specify an SNMPv1 or SNMPv2c community that will be allowed read-only
(GET and GETNEXT) or read-write (GET, GETNEXT and SET) access respectively.
By default, this will provide access to the full OID tree for such requests,
regardless of where they were sent from. The SOURCE token can be used to
restrict access to requests from the specified system(s) - see
\fIcom2sec\fR for the full details.  The OID field restricts access for
that community to the subtree rooted at the given OID, or named view.
Contexts are typically less relevant to community-based SNMP versions,
but the same behaviour applies here.
.IP "rocommunity6 COMMUNITY [SOURCE [OID | -V VIEW [CONTEXT]]]"
.IP "rwcommunity6 COMMUNITY [SOURCE [OID | -V VIEW [CONTEXT]]]"
are directives relating to requests received using IPv6
(if the agent supports such transport domains).
The interpretation of the SOURCE, OID, VIEW and CONTEXT tokens are exactly
the same as for the IPv4 versions.
.PP
In each case, only one directive should be specified for a given SNMPv3 user,
or community string.
It is \fBnot\fR appropriate to specify both \fIrouser\fR
and \fIrwuser\fR directives referring to the same SNMPv3 user (or equivalent
community settings). The \fIrwuser\fR directive provides all the access
of \fIrouser\fR (as well as allowing SET support).
The same holds true for the community-based directives.
.PP
More complex access requirements (such as access to two
or more distinct OID subtrees, or different views for GET and SET requests)
should use one of the other access control mechanisms.
Note that if several distinct communities or SNMPv3 users need to be granted
the same level of access, it would also be more efficient to use the main VACM
configuration directives.
.SS VACM Configuration
The full flexibility of the VACM is available using four configuration
directives - \fIcom2sec\fR, \fIgroup\fR, \fIview\fR and \fIaccess\fR.
These provide direct configuration of the underlying VACM tables.
.IP "com2sec  [-Cn CONTEXT] SECNAME SOURCE COMMUNITY"
.IP "com2sec6 [-Cn CONTEXT] SECNAME SOURCE COMMUNITY"
map an SNMPv1 or SNMPv2c community string to a security name - either from
a particular range of source addresses, or globally (\fI"default"\fR).
A restricted source can either be a specific hostname (or address), or
a subnet - represented as IP/MASK (e.g. 10.10.10.0/255.255.255.0), or
IP/BITS (e.g. 10.10.10.0/24), or the IPv6 equivalents.
.IP
The same community string can be specified in several separate directives
(presumably with different source tokens), and the first source/community
combination that matches the incoming request will be selected.
Various source/community combinations can also map to the same security name.
.IP
If a CONTEXT is specified (using \fI-Cn\fR), the community string will be
mapped to a security name in the named SNMPv3 context. Otherwise the
default context ("") will be used.
.IP "com2secunix [-Cn CONTEXT] SECNAME SOCKPATH COMMUNITY"
is the Unix domain sockets version of \fIcom2sec\fR.
.IP "group GROUP {v1|v2c|usm} SECNAME"
maps a security name (in the specified security model) into
a named group.  Several \fIgroup\fR directives can specify the
same group name, allowing a single access setting to apply to several 
users and/or community strings.
.IP
Note that groups must be set up for the two community-based models separately -
a single \fIcom2sec\fR (or equivalent) directive will typically be
accompanied by \fBtwo\fR \fIgroup\fR directives.
.IP "view VNAME TYPE OID [MASK]"
defines a named "view" - a subset of the overall OID tree. This is most
commonly a single subtree, but several \fIview\fR directives can be given
with the same view name (VNAME), to build up a more complex collection of OIDs.
TYPE is either \fIincluded\fR or \fIexcluded\fR, which can again define
a more complex view (e.g by excluding certain sensitive objects
from an otherwise accessible subtree).
.IP
MASK is a list of hex octets (optionally separated by '.' or ':') with
the set bits indicating which subidentifiers in the view OID to match
against.  If not specified, this defaults to matching the OID exactly
(all bits set), thus defining a simple OID subtree.  So:
.RS
.RS
view iso1 included .iso  0xf0
.br
view iso2 included .iso
.br
view iso3 included .iso.org.dod.mgmt  0xf0
.RE
.RE
.IP
would all define the same view, covering the whole of the 'iso(1)' subtree
(with the third example ignoring the subidentifiers not covered by the mask).
.IP
More usefully, the mask can be used to define a view covering a particular
row (or rows) in a table, by matching against the appropriate table index
value, but skipping the column subidentifier:
.RS
.RS
.IP "view ifRow4 included .1.3.6.1.2.1.2.2.1.0.4  0xff:a0"
.RE
.RE
.IP
Note that a mask longer than 8 bits must use ':' to separate the individual
octets.
.IP "access GROUP CONTEXT {any|v1|v2c|usm} LEVEL PREFX READ WRITE NOTIFY"
maps from a group of users/communities (with a particular security model
and minimum security level, and in a specific context) to one of three views,
depending on the request being processed.
.IP
LEVEL is one of \fInoauth\fR, \fIauth\fR, or \fIpriv\fR.
PREFX specifies how CONTEXT should be matched against the context of
the incoming request, either \fIexact\fR or \fIprefix\fR.
READ, WRITE and NOTIFY specifies the view to be used for GET*, SET
and TRAP/INFORM requests (althought the NOTIFY view is not currently used).
For v1 or v2c access, LEVEL will need to be \fInoauth\fR.
.SS Typed-View Configuration
The final group of directives extend the VACM approach into a more flexible
mechanism, which can be applied to other access control requirements. Rather than
the fixed three views of the standard VACM mechanism, this can be used to
configure various different view types.  As far as the main SNMP agent is
concerned, the two main view types are \fIread\fR and \fIwrite\fR,
corresponding to the READ and WRITE views of the main \fIaccess\fR directive.
See the 'snmptrapd.conf(5)' man page for discussion of other view types.
.IP "authcommunity TYPES  COMMUNITY   [SOURCE [OID | -V VIEW [CONTEXT]]]"
is an alternative to the \fIrocommunity\fR/\fIrwcommunity\fR directives.
TYPES will usually be \fIread\fR or \fIread,write\fR respectively.
The view specification can either be an OID subtree (as before),
or a named view (defined using the
\fIview\fR directive) for greater flexibility.  If this is omitted,
then access will be allowed to the full OID tree.
If CONTEXT is specified, access is configured within this SNMPv3 context.
Otherwise the default context ("") is used.
.IP "authuser   TYPES [-s MODEL] USER  [LEVEL [OID | -V VIEW [CONTEXT]]]"
is an alternative to the \fIrouser\fR/\fIrwuser\fR directives.
The fields TYPES, OID, VIEW and CONTEXT have the same meaning as for
\fIauthcommunity\fR.
.IP "authgroup  TYPES [-s MODEL] GROUP [LEVEL [OID | -V VIEW [CONTEXT]]]"
is a companion to the \fIauthuser\fR directive, specifying access
for a particular group (defined using the \fIgroup\fR directive as usual).
Both \fIauthuser\fR and \fIauthgroup\fR default to authenticated requests -
LEVEL can also be specified as \fInoauth\fR or \fIpriv\fR to allow
unauthenticated requests, or require encryption respectively.
Both \fIauthuser\fR and \fIauthgroup\fR directives also default to configuring
access for SNMPv3/USM requests - use the '-s' flag to specify an alternative
security model (using the same values as for \fIaccess\fR above).
.IP "authaccess TYPES [-s MODEL] GROUP VIEW [LEVEL [CONTEXT]]"
also configures the access for a particular group,
specifying the name and type of view to apply. The MODEL and LEVEL fields
are interpreted in the same way as for \fIauthgroup\fR.
If CONTEXT is specified, access is configured within this SNMPv3 context
(or contexts with this prefix if the CONTEXT field ends with '*').
Otherwise the default context ("") is used.
.IP "setaccess GROUP CONTEXT MODEL LEVEL PREFIX VIEW TYPES"
is a direct equivalent to the original \fIaccess\fR directive, typically
listing the view types as \fIread\fR or \fIread,write\fR as appropriate.
(or see 'snmptrapd.conf(5)' for other possibilities).
All other fields have the same interpretation as with \fIaccess\fR.
.SH SYSTEM INFORMATION
Most of the information reported by the Net-SNMP agent is retrieved
from the underlying system, or dynamically configured via SNMP SET requests
(and retained from one run of the agent to the next).
However, certain MIB objects can be configured or controlled via
the \fIsnmpd.conf(5)\fR file.
.SS System Group
Most of the scalar objects in the 'system' group can be configured
in this way:
.IP "sysLocation STRING"
.IP "sysContact STRING"
.IP "sysName STRING"
set the system location, system contact or system name
(\fCsysLocation.0\fR, \fCsysContact.0\fR and \fCsysName.0\fR) for the agent respectively.
Ordinarily these objects are writeable via suitably authorized SNMP SET
requests.  However, specifying one of these directives makes the
corresponding object read-only, and attempts to SET it will result in
a \fInotWritable\fR error response.
.IP "sysServices NUMBER"
sets the value of the \fCsysServices.0\fR object.
For a host system, a good value is 72 (application + end-to-end layers).
If this directive is not specified, then no value will be reported
for the \fCsysServices.0\fR object.
.IP "sysDescr STRING"
.IP "sysObjectID OID"
sets the system description or object ID for the agent.
Although these MIB objects are not SNMP-writable, these directives can be
used by a network administrator to configure suitable values for them.
.SS Interfaces Group
.IP "interface NAME TYPE SPEED"
can be used to provide appropriate type and speed settings for
interfaces where the agent fails to determine this information correctly.
TYPE is a type value as given in the IANAifType-MIB,
and can be specified numerically or by name (assuming this MIB is loaded).
.SS Host Resources Group
This requires that the agent was built with support for the
\fIhost\fR module (which is now included as part of the default build 
configuration on the major supported platforms).
.\"
.\" XXX - .IP "scandisk STRING"
.\"
.IP "ignoreDisk STRING"
controls which disk devices are scanned as part of populating the
\fChrDiskStorageTable\fR (and \fChrDeviceTable\fR).
The HostRes implementation code includes a list of disk device patterns
appropriate for the current operating system, some of which may cause
the agent to block when trying to open the corresponding disk devices.
This might lead to a timeout when walking these tables, possibly
resulting in inconsistent behaviour.  This directive can be used
to specify particular devices (either individually or wildcarded)
that should not be checked.
.RS
.IP "Note:"
Please consult the source (\fIhost/hr_disk.c\fR) and check for the
\fIAdd_HR_Disk_entry\fR calls relevant for a particular O/S
to determine the list of devices that will be scanned.
.RE
.IP
The pattern can include one or more wildcard expressions.
See \fIsnmpd.examples(5)\fR for illustration of the wildcard syntax.
.IP "skipNFSInHostResources true"
controls whether NFS and NFS-like file systems should be omitted
from the hrStorageTable (true or 1) or not (false or 0, which is the default).
If the Net-SNMP agent gets hung on NFS-mounted filesystems, you
can try setting this to '1'.
.IP "storageUseNFS [1|2]"
controls how NFS and NFS-like file systems should be reported
in the hrStorageTable.
as 'Network Disks' (1) or 'Fixed Disks' (2)
Historically, the Net-SNMP agent has reported such file systems
as 'Fixed Disks', and this is still the default behaviour.
Setting this directive to '1' reports such file systems as
\'Network Disks', as required by the Host Resources MIB.
.SS Process Monitoring 
The \fChrSWRun\fR group of the Host Resources MIB provides
information about individual processes running on the local system.
The \fCprTable\fR of the UCD-SNMP-MIB complements this by reporting
on selected services (which may involve multiple processes).
This requires that the agent was built with support for the
\fIucd-snmp/proc\fR module (which is included as part of the
default build configuration).
.IP "proc NAME [MAX [MIN]]"
monitors the number of processes called NAME (as reported by PSCMD)
running on the local system.
.IP
If the number of NAMEd processes is less than MIN or greater than MAX,
then the corresponding \fCprErrorFlag\fR instance will be
set to 1, and a suitable description message reported via the
\fCprErrMessage\fR instance.
.RS
.IP "Note:"
This situation will \fBnot\fR automatically trigger a trap to report
the problem - see the DisMan Event MIB section later.
.RE
.IP
If neither MAX nor MIN are specified (or are both 0), they will
default to \fBinfinity\fR and 1 respectively ("at least one").
If only MAX is specified, MIN will default to 0 ("no more than MAX").
.IP "procfix NAME PROG ARGS"
registers a command that can be run to fix errors with the given
process NAME.  This will be invoked when the corresponding
\fCprErrFix\fR instance is set to 1.
.RS
.IP "Note:"
This command will \fBnot\fR be invoked automatically.
.\" XXX - but see the DisMan Event MIB section later ???
.RE
.IP
The \fIprocfix\fR directive must be specified \fBafter\fR the matching
\fIproc\fR directive, and cannot be used on its own.
.PP
If no \fIproc\fR directives are defined, then walking the
\fCprTable\fR will fail (\fInoSuchObject\fI).
.SS Disk Usage Monitoring
This requires that the agent was built with support for the
\fIucd-snmp/disk\fR module (which is included as part of the
default build configuration).
.IP "disk PATH [ MINSPACE | MINPERCENT% ]"
monitors the disk mounted at PATH for available disk space.
.IP
The minimum threshold can either be specified in kB (MINSPACE) or
as a percentage of the total disk (MINPERCENT% with a '%' character),
defaulting to 100kB if neither are specified.
If the free disk space falls below this threshold, 
then the corresponding \fCdskErrorFlag\fR instance will be
set to 1, and a suitable description message reported via the
\fCdskErrorMsg\fR instance.
.RS
.IP "Note:"
This situation will \fBnot\fR automatically trigger a trap to report
the problem - see the DisMan Event MIB section later.
.RE
.IP "includeAllDisks MINPERCENT%"
configures monitoring of all disks found on the system,
using the specified (percentage) threshold.
The threshold for individual disks can be adjusted using suitable
\fIdisk\fR directives (which can come either before or after the
\fIincludeAllDisks\fR directive).
.RS
.IP "Note:"
Whether \fIdisk\fR directives appears before or after \fIincludeAllDisks\fR 
may affect the indexing of the \fCdskTable\fR.
.RE
.IP
Only one \fIincludeAllDisks\fR directive should be specified - any
subsequent copies will be ignored.
.IP
The list of mounted disks will be determined when the agent starts using the
setmntent(3) and getmntent(3), or fopen(3) and getmntent(3),  or
setfsent(3)  and  getfsent(3) system calls. If none of the above
system calls are available then the root partition  "/"
(which  is  assumed to exist on any UNIX based system) will be monitored.
Disks mounted after the agent has started will not be monitored.
.\"
.\" XXX - unless the config is re-read ??
.\"
.PP
If neither any \fIdisk\fR directives or \fIincludeAllDisks\fR are defined,
then walking the \fCdskTable\fR will fail (\fInoSuchObject\fI).
.SS System Load Monitoring
This requires that the agent was built with support for either the
\fIucd-snmp/loadave\fR module or the \fIucd-snmp/memory\fR module
respectively (both of which are included as part of the
default build configuration).
.IP "load MAX1 [MAX5 [MAX15]]"
monitors the load average of the local system, specifying
thresholds for the 1-minute, 5-minute and 15-minute averages.
If any of these loads exceed the associated maximum value, 
then the corresponding \fClaErrorFlag\fR instance will be
set to 1, and a suitable description message reported via the
\fClaErrMessage\fR instance.
.RS
.IP "Note:"
This situation will \fBnot\fR automatically trigger a trap to report
the problem - see the DisMan Event MIB section later.
.RE
.IP
If the MAX15 threshold is omitted, it will default to the MAX5 value.
If both MAX5 and MAX15 are omitted, they will default to the MAX1 value.
If this directive is not specified, all three thresholds will
default to a value of DEFMAXLOADAVE.
.IP
If a threshold value of 0 is given, the agent will not report errors
via the relevant \fClaErrorFlag\fR or \fClaErrMessage\fR instances,
regardless of the current load.
.PP
Unlike the \fIproc\fR and \fIdisk\fR directives, walking the
walking the \fClaTable\fR will succeed (assuming the
\fIucd-snmp/loadave\fR module was configured into the agent),
even if the \fIload\fR directive is not present.
.IP "swap MIN "
monitors the amount of swap space available on the local system.
If this falls below the specified threshold (MIN kB),
then the \fImemErrorSwap\fR object will be set to 1,
and a suitable description message reported via \fImemSwapErrorMsg\fR.
.RS
.IP "Note:"
This situation will \fBnot\fR automatically trigger a trap to report
the problem - see the DisMan Event MIB section later.
.RE
If this directive is not specified, the default threshold is 16 MB.
.SS Log File Monitoring
This requires that the agent was built with support for either the
\fIucd-snmp/file\fR or \fIucd-snmp/logmatch\fR modules respectively
(both of which are included as part of the
default build configuration).
.IP "file FILE [MAXSIZE]"
monitors the size of the specified file (in kB).
If MAXSIZE is specified, and the size of the file exceeds
this threshold, then the corresponding \fCfileErrorFlag\fR
instance will be set to 1, and a suitable description message reported
via the \fCfileErrorMsg\fR instance.
.RS
.IP "Note:"
This situation will \fBnot\fR automatically trigger a trap to report
the problem - see the DisMan Event MIB section later.
.RE
.IP
Note: A maximum of 20 files can be monitored.
.IP
Note: If no \fIfile\fR directives are defined, then walking the
\fCfileTable\fR will fail (\fInoSuchObject\fR).
.IP "logmatch NAME FILE CYCLETIME REGEX"
monitors the specified file for occurances of the specified
pattern REGEX. The file position is stored internally so the entire file
is only read initially, every subsequent pass will only read the new lines
added to the file since the last read.
.RS
.IP NAME
name of the logmatch instance (will appear as logMatchName under
logMatch/logMatchTable/logMatchEntry/logMatchName in the ucd-snmp MIB tree)
.IP FILE
absolute path to the logfile to be monitored. Note that this path
can contain date/time directives (like in the UNIX 'date' command). See the
manual page for 'strftime' for the various directives accepted.
.IP CYCLETIME
time interval for each logfile read and internal variable update in seconds.
Note: an SNMPGET* operation will also trigger an immediate logfile read and
variable update.
.IP REGEX
the regular expression to be used. Note: DO NOT enclose the regular expression
in quotes even if there are spaces in the expression as the quotes will also
become part of the pattern to be matched!
.RE
.IP
Example:
.RS
.IP
logmatch apache-GETs /usr/local/apache/logs/access.log-%Y-%m-%d 60 GET.*HTTP.*
.IP
This logmatch instance is named 'apache-GETs', uses 'GET.*HTTP.*' as its
regular expression and it will monitor the file named
(assuming today is May 6th 2009): '/usr/local/apache/logs/access.log-2009-05-06',
tomorrow it will look for 'access.log-2009-05-07'. The logfile is read every 60
seconds.
.RE
.IP
Note: A maximum of 250 logmatch directives can be specified.
.IP
Note: If no \fIlogmatch\fR directives are defined, then walking the
\fClogMatchTable\fR will fail (\fInoSuchObject\fI).
.SH "ACTIVE MONITORING"
The usual behaviour of an SNMP agent is to wait for incoming SNMP requests
and respond to them - if no requests are received, an agent will typically
not initiate any actions. This section describes various directives that
can configure \fIsnmpd\fR to take a more active role.
.SS "Notification Handling"
.IP "trapcommunity STRING"
defines the default community string to be used when sending traps.
Note that this directive must be used prior to any community-based
trap destination directives that need to use it.
.IP "trapsink HOST [COMMUNITY [PORT]]"
.IP "trap2sink HOST [COMMUNITY [PORT]]"
.IP "informsink HOST [COMMUNITY [PORT]]"
define the address of a notification receiver that should be sent
SNMPv1 TRAPs, SNMPv2c TRAP2s, or SNMPv2 INFORM notifications respectively.
See the section 
.B LISTENING ADDRESSES
in the
.I snmpd(8)
manual page for more information about the format of listening
addresses.
If COMMUNITY is not specified, the most recent \fItrapcommunity\fR
string will be used.
.IP
If the transport address does not include an explicit
port specification, then PORT will be used.
If this is not specified, the well known SNMP trap
port (162) will be used.
.RS
.IP Note:
This mechanism is being deprecated, and the listening port
should be specified via the transport specification HOST instead.
.RE
.IP
If several sink directives are specified, multiple
copies of each notification (in the appropriate formats)
will be generated.
.RS
.IP Note:
It is \fBnot\fR normally appropriate to list two (or all three)
sink directives with the same destination.
.RE
.IP "trapsess [SNMPCMD_ARGS] HOST"
provides a more generic mechanism for defining notification destinations.
.I "SNMPCMD_ARGS"
should be the command-line options required for an equivalent
\fIsnmptrap\fR (or \fIsnmpinform\fR) command to send the desired notification.
The option \fI-Ci\fR can be used (with \fI-v2c\fR or \fI-v3\fR) to generate
an INFORM notification rather than an unacknowledged TRAP.
.IP
This is the appropriate directive for defining SNMPv3 trap receivers.
See
http://www.net-snmp.org/tutorial/tutorial-5/commands/snmptrap-v3.html
for more information about SNMPv3 notification behaviour.
.IP "authtrapenable {1|2}"
determines whether to generate authentication failure traps
(\fIenabled(1)\fR) or not (\fIdisabled(2)\fR - the default).
Ordinarily the corresponding MIB
object (\fCsnmpEnableAuthenTraps.0\fR) is read-write, but specifying
this directive makes this object read-only, and attempts to set the
value via SET requests will result in a \fInotWritable\fR error response.
.SS "DisMan Event MIB"
The previous directives can be used to configure where traps should
be sent, but are not concerned with \fIwhen\fR to send such traps
(or what traps should be generated).  This is the domain of the
Event MIB - developed by the Distributed Management (DisMan)
working group of the IETF.
.PP
This requires that the agent was built with support for the
\fIdisman/event\fR module (which is now included as part of the
default build configuration for the most recent distribution).
.RS
.IP "Note:"
The behaviour of the latest implementation differs in some minor
respects from the previous code - nothing too significant, but
existing scripts may possibly need some minor adjustments.
.RE
.IP "iquerySecName NAME"
.IP "agentSecName NAME"
specifies the default SNMPv3 username, to be used when making internal
queries to retrieve any necessary information (either for evaluating
the monitored expression, or building a notification payload).
These internal queries always use SNMPv3, even if normal querying
of the agent is done using SNMPv1 or SNMPv2c.
.IP
Note that this user must also be explicitly created (\fIcreateUser\fR)
and given appropriate access rights (e.g. \fIrouser\fR).  This
directive is purely concerned with defining \fIwhich\fR user should
be used - not with actually setting this user up.
.\"
.\" XXX - Should it create the user as well?
.\"
.\" .IP "iqueryVersion "
.\" .IP "iquerySecLevel "
.\"
.IP "monitor [OPTIONS] NAME EXPRESSION"
defines a MIB object to monitor.
If the EXPRESSION condition holds (see below), then this will trigger
the corresponding event, and either send a notification or apply
a SET assignment (or both).
Note that the event will only be triggered once, when the expression
first matches.  This monitor entry will not fire again until the
monitored condition first becomes false, and then matches again.
NAME is an administrative name for this expression, and is used for
indexing the \fCmteTriggerTable\fR (and related tables).
Note also that such monitors use an internal SNMPv3 request to retrieve
the values being monitored (even if normal agent queries typically use
SNMPv1 or SNMPv2c).  See the \fIiquerySecName\fP token described above.
.IP "\fIEXPRESSION\fR"
There are three types of monitor expression supported by the Event MIB -
existence, boolean and threshold tests.
.RS
.IP "OID | ! OID | != OID"
defines an \fIexistence(0)\fR monitor test.
A bare OID specifies a \fIpresent(0)\fR test, which will fire when
(an instance of) the monitored OID is created.
An expression of the form \fI! OID\fR specifies an \fIabsent(1)\fR test,
which will fire when the monitored OID is delected.
An expression of the form \fI!= OID\fR specifies a \fIchanged(2)\fR test,
which will fire whenever the monitored value(s) change.
Note that there \fBmust\fP be whitespace before the OID token.
.IP "OID OP VALUE"
defines a \fIboolean(1)\fR monitor test.
OP should be one of the defined
comparison operators (!=, ==, <, <=, >, >=) and VALUE should be an
integer value to compare against.
Note that there \fBmust\fP be whitespace around the OP token.
A comparison such as \fCOID !=0\fP will not be handled correctly.
.IP "OID MIN MAX [DMIN DMAX]"
defines a \fIthreshold(2)\fR monitor test.
MIN and MAX are integer values, specifying lower and upper thresholds.
If the value of the monitored OID falls below the lower threshold (MIN)
or rises above the upper threshold (MAX), then the monitor entry will
trigger the corresponding event.
.IP
Note that the rising threshold event will only be re-armed when
the monitored value falls below the \fBlower\fR threshold (MIN).
Similarly, the falling threshold event will be re-armed by
the upper threshold (MAX).
.IP
The optional parameters DMIN and DMAX configure a pair of
similar threshold tests, but working with the delta
differences between successive sample values.
.RE
.IP "\fIOPTIONS\fR"
There are various options to control the behaviour of the monitored
expression.  These include:
.RS
.IP "-D"
indicates that the expression should be evaluated using delta differences
between sample values (rather than the values themselves).
.IP "-d OID"
.IP "-di OID"
specifies a discontinuity marker for validating delta differences.
A \fI-di\fR object instance will be used exactly as given.
A \fI-d\fR object will have the instance subidentifiers from the
corresponding (wildcarded) expression object appended.
If the \fI-I\fR flag is specified, then there is no difference
between these two options.
.IP
This option also implies \fI-D\fR.
.IP "-e EVENT"
specifies the event to be invoked when this monitor entry is triggered.
If this option is not given, the monitor entry will generate one
of the standard notifications defined in the DISMAN-EVENT-MIB.
.IP "-I"
indicates that the monitored expression should be applied to the
specified OID as a single instance.  By default, the OID will
be treated as a wildcarded object, and the monitor expanded
to cover all matching instances.
.IP "-i OID"
.IP "-o OID"
define additional varbinds to be added to the notification payload
when this monitor trigger fires.
For a wildcarded expression, the suffix of the matched instance
will be added to any OIDs specified using \fI-o\fR, while OIDs
specified using \fI-i\fR will be treated as exact instances.
If the \fI-I\fR flag is specified, then there is no difference
between these two options.
.IP
See \fIstrictDisman\fR for details of the ordering of notification payloads.
.IP "-r FREQUENCY"
monitors the given expression every FREQUENCY seconds.
By default, the expression will be evaluated every 600s (10 minutes). 
.IP "-S"
indicates that the monitor expression should \fInot\fR be evaluated
when the agent first starts up.  The first evaluation will be done
once the first repeat interval has expired.
.IP "-s"
indicates that the monitor expression \fIshould\fR be evaluated when the
agent first starts up.  This is the default behaviour.
.RS
.IP "Note:"
Notifications triggered by this initial evaluation will be sent
\fIbefore\fR the \fCcoldStart\fR trap.
.RE
.IP "-u SECNAME"
specifies a security name to use for scanning the local host,
instead of the default \fIiquerySecName\fR.
Once again, this user must be explicitly created and given
suitable access rights.
.RE
.IP "notificationEvent ENAME NOTIFICATION [-m] [-i OID | -o OID ]*"
defines a notification event named ENAME.
This can be triggered from a given \fImonitor\fR entry by specifying
the option \fI-e ENAME\fR (see above).
NOTIFICATION should be the OID of the NOTIFICATION-TYPE definition
for the notification to be generated.
.IP
If the \fI-m\fR option is given, the notification payload will
include the standard varbinds as specified in the OBJECTS clause
of the notification MIB definition.
This option must come \fBafter\fR the NOTIFICATION OID
(and the relevant MIB file must be available and loaded by the agent).
Otherwise, these varbinds must
be listed explicitly (either here or in the corresponding
\fImonitor\fR directive).
.IP
The \fI-i OID\fR and \fI-o OID\fR options specify additional
varbinds to be appended to the notification payload, after the
standard list.
If the monitor entry that triggered this event involved a
wildcarded expression, the suffix of the matched instance
will be added to any OIDs specified using \fI-o\fR, while OIDs
specified using \fI-i\fR will be treated as exact instances.
If the \fI-I\fR flag was specified to the \fImonitor\fR directive,
then there is no difference between these two options.
.IP "setEvent ENAME [-I] OID = VALUE "
defines a set event named ENAME, assigning the (integer) VALUE
to the specified OID.
This can be triggered from a given \fImonitor\fR entry by specifying
the option \fI-e ENAME\fR (see above).
.IP
If the monitor entry that triggered this event involved a
wildcarded expression, the suffix of the matched instance
will normally be added to the OID.
If the \fI-I\fR flag was specified to either of the
\fImonitor\fR or \fIsetEvent\fR directives, the
specified OID will be regarded as an exact single instance.
.IP "strictDisman yes"
The definition of SNMP notifications states that the
varbinds defined in the OBJECT clause should come first
(in the order specified), followed by any "extra" varbinds
that the notification generator feels might be useful.
The most natural approach would be to associate these
mandatory varbinds with the \fInotificationEvent\fR entry,
and append any varbinds associated with the monitor entry
that triggered the notification to the end of this list.
This is the default behaviour of the Net-SNMP Event MIB implementation.
.IP
Unfortunately, the DisMan Event MIB specifications actually
state that the trigger-related varbinds should come \fBfirst\fR,
followed by the event-related ones.  This directive can be used to
restore this strictly-correct (but inappropriate) behaviour.
.RS
.IP "Note:"
Strict DisMan ordering may result in generating invalid notifications
payload lists if the \fInotificationEvent -n\fR flag is used together
with \fImonitor -o\fR (or \fI-i\fR) varbind options.
.RE
.IP
If no \fImonitor\fR entries specify payload varbinds,
then the setting of this directive is irrelevant.
.IP "linkUpDownNotifications yes"
will configure the Event MIB tables to monitor the \fCifTable\fR
for network interfaces being taken up or down, and triggering
a \fIlinkUp\fR or \fIlinkDown\fR notification as appropriate.
.IP
This is exactly equivalent to the configuration:
.RS
.IP
.nf
notificationEvent  linkUpTrap    linkUp   ifIndex ifAdminStatus ifOperStatus
notificationEvent  linkDownTrap  linkDown ifIndex ifAdminStatus ifOperStatus

monitor  -r 60 -e linkUpTrap   "Generate linkUp" ifOperStatus != 2
monitor  -r 60 -e linkDownTrap "Generate linkDown" ifOperStatus == 2
.fi
.RE
.IP "defaultMonitors yes"
will configure the Event MIB tables to monitor the various
\fCUCD-SNMP-MIB\fR tables for problems (as indicated by
the appropriate \fCxxErrFlag\fR column objects).
.IP
This is exactly equivalent to the configuration:
.RS
.IP
.nf
monitor	-o prNames -o prErrMessage "process table" prErrorFlag != 0
monitor	-o memErrorName -o memSwapErrorMsg "memory" memSwapError != 0
monitor	-o extNames -o extOutput "extTable" extResult != 0
monitor	-o dskPath -o dskErrorMsg "dskTable" dskErrorFlag != 0
monitor	-o laNames -o laErrMessage  "laTable" laErrorFlag != 0
monitor	-o fileName -o fileErrorMsg  "fileTable" fileErrorFlag != 0
.fi
.RE
.PP
In both these latter cases, the snmpd.conf must also contain a
\fIiquerySecName\fR directive, together with a corresponding
\fIcreateUser\fR entry and suitable access control configuration.
.SS "DisMan Schedule MIB"
The DisMan working group also produced a mechanism for scheduling
particular actions (a specified SET assignment) at given times.
This requires that the agent was built with support for the
\fIdisman/schedule\fR module (which is included as part of the
default build configuration for the most recent distribution).
.PP
There are three ways of specifying the scheduled action:
.IP "repeat FREQUENCY OID = VALUE"
configures a SET assignment of the (integer) VALUE to the MIB instance
OID, to be run every FREQUENCY seconds.
.IP "cron MINUTE HOUR DAY MONTH WEEKDAY  OID = VALUE"
configures a SET assignment of the (integer) VALUE to the MIB instance
OID, to be run at the times specified by the fields MINUTE to WEEKDAY.
These follow the same pattern as the equivalent \fIcrontab(5)\fR fields.
.RS
.IP "Note:"
These fields should be specified as a (comma-separated) list of numeric
values.  Named values for the MONTH and WEEKDAY fields are not supported,
and neither are value ranges. A wildcard match can be specified as '*'.
.RE
.IP
The DAY field can also accept negative values, to indicate days counting
backwards from the end of the month.
.IP "at MINUTE HOUR DAY MONTH WEEKDAY  OID = VALUE"
configures a one-shot SET assignment, to be run at the first matching
time as specified by the fields MINUTE to WEEKDAY.  The interpretation
of these fields is exactly the same as for the \fIcron\fR directive.
.SH "EXTENDING AGENT FUNCTIONALITY"
One of the first distinguishing features of the original UCD suite was
the ability to extend the functionality of the agent - not just by
recompiling with code for new MIB modules, but also by configuring the running agent to
report additional information. There are a number of techniques to
support this, including:
.IP \(bu
running external commands (\fIexec\fR, \fIextend\fR, \fIpass\fR)
.IP \(bu
loading new code dynamically (embedded perl, \fIdlmod\fR)
.IP \(bu
communicating with other agents (\fIproxy\fR, SMUX, AgentX)
.SS "Arbitrary Extension Commands"
The earliest extension mechanism was the ability to run arbitrary
commands or shell scripts. Such commands do not need to be aware of
SNMP operations, or conform to any particular behaviour - the MIB
structures are designed to accommodate any form of command output.
Use of this mechanism requires that the agent was built with support for the
\fIucd-snmp/extensible\fR and/or \fIagent/extend\fR modules (which
are both included as part of the default build configuration).
.IP "exec [MIBOID] NAME PROG ARGS"
.IP "sh [MIBOID] NAME PROG ARGS"
invoke the named PROG with arguments of ARGS.  By default the exit
status and first line of output from the command will be reported via
the \fCextTable\fR, discarding any additional output.
.RS
.IP Note:
Entries in this table appear in the order they are read from the
configuration file.  This means that adding new \fIexec\fR (or \fIsh\fR)
directives and restarting the agent, may affect the indexing of other
entries.
.RE
.IP
The PROG argument for \fIexec\fR directives must be a full path
to a real binary, as it is executed via the exec() system call.
To invoke a shell script, use the \fIsh\fR directive instead.
.IP
If MIBOID is specified, then the results will be rooted at this point
in the OID tree, returning the exit statement as MIBOID.ERRORFLAG.0
and the entire command output in a pseudo-table based at
MIBNUM.ERRORMSG - with one 'row' for each line of output.
.RS
.IP Note:
The layout of this "relocatable" form of \fIexec\fR (or \fIsh\fR) output
does not strictly form a valid MIB structure.  This mechanism is being
deprecated - please see the \fIextend\fR directive (described below) instead.
.RE
.IP
The agent does not cache the exit status or output of the executed program.
.\"
.\" XXX - Is this still true ??
.\"
.IP "execfix NAME PROG ARGS"
registers a command that can be invoked on demand - typically to respond
to or fix errors with the corresponding \fIexec\fR or \fIsh\fR entry.
When the \fIextErrFix\fR instance for a given NAMEd entry is set to the
integer value of 1, this command will be called.
.RS
.IP "Note:"
This directive can only be used in combination with a corresponding
\fIexec\fR or \fIsh\fR directive, which must be defined first.
Attempting to define an unaccompanied \fIexecfix\fR directive will fail.
.RE
.PP
\fIexec\fR and \fIsh\fR extensions can only be configured via the
snmpd.conf file.  They cannot be set up via SNMP SET requests.
.IP "extend [MIBOID] NAME PROG ARGS"
works in a similar manner to the \fIexec\fR directive, but with a number
of improvements.  The MIB tables (\fInsExtendConfigTable\fR
etc) are indexed by the NAME token, so are unaffected by the order in
which entries are read from the configuration files.
There are \fItwo\fR result tables - one (\fInsExtendOutput1Table\fR)
containing the exit status, the first line and full output (as a single string)
for each \fIextend\fR entry, and the other (\fInsExtendOutput2Table\fR)
containing the complete output as a series of separate lines.
.IP
If MIBOID is specified, then the configuration and result tables will be rooted
at this point in the OID tree, but are otherwise structured in exactly
the same way. This means that several separate \fIextend\fR
directives can specify the same MIBOID root, without conflicting.
.IP
The exit status and output is cached for each entry individually, and
can be cleared (and the caching behaviour configured)
using the \fCnsCacheTable\fR.
.IP "extendfix NAME PROG ARGS"
registers a command that can be invoked on demand, by setting the
appropriate \fInsExtendRunType\fR instance to the value
\fIrun-command(3)\fR.  Unlike the equivalent \fIexecfix\fR,
this directive does not need to be paired with a corresponding
\fIextend\fR entry, and can appear on its own.
.PP
Both \fIextend\fR and \fIextendfix\fR directives can be configured
dynamically, using SNMP SET requests to the NET-SNMP-EXTEND-MIB.
.SS "MIB-Specific Extension Commands"
The first group of extension directives invoke arbitrary commands,
and rely on the MIB structure (and management applications) having
the flexibility to accommodate and interpret the output.  This is a
convenient way to make information available quickly and simply, but
is of no use when implementing specific MIB objects, where the extension
must conform to the structure of the MIB (rather than vice versa).
The remaining extension mechanisms are all concerned with such
MIB-specific situations - starting with "pass-through" scripts.
Use of this mechanism requires that the agent was built with support for the
\fIucd-snmp/pass\fR and \fIucd-snmp/pass_persist\fR modules (which
are both included as part of the default build configuration).
.IP "pass [-p priority] MIBOID PROG"
will pass control of the subtree rooted at MIBOID to the specified
PROG command.  GET and GETNEXT requests for OIDs within this tree will
trigger this command, called as:
.RS
.IP
PROG -g OID
.IP
PROG -n OID
.RE
.IP
respectively, where OID is the requested OID.
The PROG command should return the response varbind as three separate
lines printed to stdout - the first line should be the OID of the returned
value, the second should be its TYPE (one of the text strings
.B integer, gauge, counter, timeticks, ipaddress, objectid,
or
.B string
), and the third should be the value itself.
.IP
If the command cannot return an appropriate varbind - e.g the specified
OID did not correspond to a valid instance for a GET request, or there
were no following instances for a GETNEXT - then it should exit without
producing any output.  This will result in an SNMP \fInoSuchName\fR
error, or a \fInoSuchInstance\fR exception.
.RS
.RS
.IP "Note:"
The SMIv2 type \fBcounter64\fR
and SNMPv2 \fInoSuchObject\fR exception are not supported.
.RE
.RE
.IP
A SET request will result in the command being called as:
.RS
.IP
PROG -s OID TYPE VALUE
.RE
.IP
where TYPE is one of the tokens listed above, indicating the type of the
value passed as the third parameter.
.\".RS
.\".RS
.\".IP "Note:"
.\".B counter
.\"(and
.\".B counter64
.\") syntax objects are not valid for SETs
.\".RE
.\".RE
.IP
If the assignment is successful, the PROG command should exit without producing
any output. Errors should be indicated by writing one of the strings
.B not-writable, 
or 
.B wrong-type
to stdout,
and the agent will generate the appropriate error response.
.RS
.RS
.IP "Note:"
The other SNMPv2 errors are not supported.
.RE
.RE
.IP
In either case, the command should exit once it has finished processing.
Each request (and each varbind within a single request) will trigger
a separate invocation of the command.
.IP
The default registration priority is 127.  This can be
changed by supplying the optional -p flag, with lower priority
registrations being used in preference to higher priority values.
.IP "pass_persist [-p priority] MIBOID PROG"
will also pass control of the subtree rooted at MIBOID to the specified
PROG command.  However this command will continue to run after the initial
request has been answered, so subsequent requests can be processed without
the startup overheads.
.IP
Upon initialization, PROG will be passed the string "PING\\n" on stdin,
and should respond by printing "PONG\\n" to stdout.
.IP
For GET and GETNEXT requests, PROG will be passed two lines on stdin,
the command (\fIget\fR or \fIgetnext\fR) and the requested OID.
It should respond by printing three lines to stdout - 
the OID for the result varbind, the TYPE and the VALUE itself -
exactly as for the \fIpass\fR directive above.
If the command cannot return an appropriate varbind,
it should print print "NONE\\n" to stdout (but continue running).
.IP
For SET requests, PROG will be passed three lines on stdin,
the command (\fIset\fR) and the requested OID,
followed by the type and value (both on the same line).
If the assignment is successful, the command should print
"DONE\\n" to stdout.
Errors should be indicated by writing one of the strings
.B not-writable, 
.B wrong-type,
.B wrong-length,
.B wrong-value
or
.B inconsistent-value
to stdout,
and the agent will generate the appropriate error response.
In either case, the command should continue running.
.IP
The registration priority can be changed using the optional
-p flag, just as for the \fIpass\fR directive.
.PP
\fIpass\fR and \fIpass_persist\fR extensions can only be configured via the
snmpd.conf file.  They cannot be set up via SNMP SET requests.
.\"
.\" XXX - caching ??
.\"
.SS "Embedded Perl Support"
Programs using the previous extension mechanisms can be written in any convenient
programming language - including perl, which is a common choice for
pass-through extensions in particular.  However the Net-SNMP agent
also includes support for embedded perl technology (similar to
\fImod_perl\fR for the Apache web server).  This allows the agent
to interpret perl scripts directly, thus avoiding the overhead of
spawning processes and initializing the perl system when a request is received.
.PP
Use of this mechanism requires that the agent was built with support for the embedded
perl mechanism, which is not part of the default build environment. It
must be explicitly included by specifying the '--enable-embedded-perl'
option to the configure script when the package is first built.
.PP
If enabled, the following directives will be recognised:
.IP "disablePerl true"
will turn off embedded perl support entirely (e.g. if there are problems
with the perl installation).
.IP "perlInitFile FILE"
loads the specified initialisation file (if present)
immediately before the first \fIperl\fR directive is parsed.
If not explicitly specified, the agent will look for the default
initialisation file DATADIR/snmp/snmp_perl.pl.
.IP
The default initialisation file
creates an instance of a \fCNetSNMP::agent\fR object - a variable
\fC$agent\fR which can be used to register perl-based MIB handler routines.
.IP "perl EXPRESSION"
evaluates the given expression.  This would typically register a
handler routine to be called when a section of the OID tree was
requested:
.RS
.RS
.nf
\fCperl use Data::Dumper;
perl sub myroutine  { print "got called: ",Dumper(@_),"\\n"; }
perl $agent->register('mylink', '.1.3.6.1.8765', \\&myroutine);\fR
.fi
.RE
.RE
.IP
This expression could also source an external file:
.RS
.RS
\fCperl 'do /path/to/file.pl';\fR
.RE
.RE
.IP
or perform any other perl-based processing that might be required.
.\"
.\" Link to more examples
.\"
.SS Dynamically Loadable Modules
Most of the MIBs supported by the Net-SNMP agent are implemented as
C code modules, which were compiled and linked into the agent libraries
when the suite was first built.  Such implementation modules can also be
compiled independently and loaded into the running agent once it has
started.  Use of this mechanism requires that the agent was built with support for the
\fIucd-snmp/dlmod\fR module (which is included as part of the default
build configuration).
.IP "dlmod NAME PATH"
will load the shared object module from the file PATH (an absolute
filename), and call the initialisation routine \fIinit_NAME\fR.
.RS
.IP "Note:"
If the specified PATH is not a fully qualified filename, it will
be interpreted relative to LIBDIR/snmp/dlmod, and \fC.so\fR
will be appended to the filename.
.RE
.PP
This functionality can also be configured using SNMP SET requests
to the UCD-DLMOD-MIB.
.SS "Proxy Support"
Another mechanism for extending the functionality of the agent
is to pass selected requests (or selected varbinds) to another
SNMP agent, which can be running on the same host (presumably
listening on a different port), or on a remote system.
This can be viewed either as the main agent delegating requests to
the remote one, or acting as a proxy for it.
Use of this mechanism requires that the agent was built with support for the
\fIucd-snmp/proxy\fR module (which is included as part of the
default build configuration).
.IP "proxy [-Cn CONTEXTNAME] [SNMPCMD_ARGS] HOST OID [REMOTEOID]"
will pass any incoming requests under OID to the agent listening
on the port specified by the transport address HOST.
See the section 
.B LISTENING ADDRESSES
in the
.I snmpd(8)
manual page for more information about the format of listening
addresses.
.RS
.IP "Note:"
To proxy the entire MIB tree, use the OID .1.3
(\fBnot\fR the top-level .1)
.RE
.PP
The \fISNMPCMD_ARGS\fR should provide sufficient version and
administrative information to generate a valid SNMP request
(see \fIsnmpcmd(1)\fR).
.IP "Note:"
The proxied request will \fInot\fR use the administrative
settings from the original request.
.RE
.PP
If a CONTEXTNAME is specified, this will register the proxy
delegation within the named context in the local agent.
Defining multiple \fIproxy\fR directives for the same OID but
different contexts can be used to query several remote agents
through a single proxy, by specifying the appropriate SNMPv3
context in the incoming request (or using suitable configured
community strings - see the \fIcom2sec\fR directive).
.PP
Specifying the REMOID parameter will map the local MIB tree
rooted at OID to an equivalent subtree rooted at REMOID
on the remote agent.
.SS SMUX Sub-Agents
The Net-SNMP agent supports the SMUX protocol (RFC 1227) to communicate
with SMUX-based subagents (such as \fIgated\fR, \fIzebra\fR or \fIquagga\fR).
Use of this mechanism requires that the agent was built with support for the
\fIsmux\fR module, which is not part of the default build environment, and
must be explicitly included by specifying the '--with-mib-modules=smux'
option to the configure script when the package is first built.
.RS
.IP "Note:"
This extension protocol has been officially deprecated in
favour of AgentX (see below).
.RE
.IP "smuxpeer OID PASS"
will register a subtree for SMUX-based processing, to be
authenticated using the password PASS.  If a subagent
(or "peer") connects to the agent and registers this subtree
.\"
.\" Or a subtree of this subtree ??
.\"
then requests for OIDs within it will be passed to that
SMUX subagent for processing.
.IP
A suitable entry for an OSPF routing daemon (such as \fIgated\fR,
\fIzebra\fR or \fIquagga\fR) might be something like
.RS
.RS
.I smuxpeer .1.3.6.1.2.1.14 ospf_pass
.RE
.RE
.IP "smuxsocket <IPv4-address>"
defines the IPv4 address for SMUX peers to communicate with the Net-SNMP agent.
The default is to listen on all IPv4 interfaces ("0.0.0.0"), unless the 
package has been configured with "--enable-local-smux" at build time, which 
causes it to only listen on 127.0.0.1 by default. SMUX uses the well-known
TCP port 199.
.PP
Note the Net-SNMP agent will only operate as a SMUX \fImaster\fR
agent. It does not support acting in a SMUX subagent role.
.SS AgentX Sub-Agents
The Net-SNMP agent supports the AgentX protocol (RFC 2741) in
both master and subagent roles.
Use of this mechanism requires that the agent was built with support for the
\fIagentx\fR module (which is included as part of the
default build configuration), and also that this support is
explicitly enabled (e.g. via the \fIsnmpd.conf\fR file).
.PP
There are two directives specifically relevant to running as
an AgentX master agent:
.IP "master agentx"
will enable the AgentX functionality and cause the agent to
start listening for incoming AgentX registrations.
This can also be activated by specifying the '-x' command-line
option (to specify an alternative listening socket).
.IP "agentXPerms SOCKPERMS [DIRPERMS [USER|UID [GROUP|GID]]]"
Defines the permissions and ownership of the AgentX Unix Domain socket,
and the parent directories of this socket.
SOCKPERMS and DIRPERMS must be octal digits (see 
.I chmod(1)
). By default this socket will only be accessible to subagents which 
have the same userid as the agent.
.PP
There is one directive specifically relevant to running as
an AgentX sub-agent:
.IP "agentXPingInterval NUM"
will make the subagent try and reconnect every NUM seconds to the
master if it ever becomes (or starts) disconnected.
.PP
The remaining directives are relevant to both AgentX master
and sub-agents:
.IP "agentXSocket [<transport-specifier>:]<transport-address>[,...]"
defines the address the master agent listens at, or the subagent
should connect to.
The default is the Unix Domain socket \fCAGENTX_SOCKET\fR.
Another common alternative is \fCtcp:localhost:705\fR.
See the section
.B LISTENING ADDRESSES
in the
.I snmpd(8)
manual page for more information about the format of addresses.
.RS
.IP "Note:"
Specifying an AgentX socket does \fBnot\fR automatically enable
AgentX functionality (unlike the '-x' command-line option).
.RE
.IP "agentXTimeout NUM"
defines the timeout period (NUM seconds) for an AgentX request.
Default is 1 second.
.IP "agentXRetries NUM"
defines the number of retries for an AgentX request.
Default is 5 retries.
.PP
net-snmp ships with both C and Perl APIs to develop your own AgentX
subagent.
.SH "OTHER CONFIGURATION"
.IP "override [-rw] OID TYPE VALUE"
This directive allows you to override a particular OID with a
different value (and possibly a different type of value).  The -rw
flag will allow snmp SETs to modify it's value as well. (note that if
you're overriding original functionality, that functionality will be
entirely lost.  Thus SETS will do nothing more than modify the
internal overridden value and will not perform any of the original
functionality intended to be provided by the MIB object.  It's an
emulation only.)  An example:
.RS
.IP
\fCoverride sysDescr.0 octet_str "my own sysDescr"\fR
.RE
.IP
That line will set the sysDescr.0 value to "my own sysDescr" as well
as make it modifiable with SNMP SETs as well (which is actually
illegal according to the MIB specifications).
.IP
Note that care must be taken when using this.  For example, if you try
to override a property of the 3rd interface in the ifTable with a new
value and later the numbering within the ifTable changes it's index
ordering you'll end up with problems and your modified value won't
appear in the right place in the table.
.IP
Valid TYPEs are: integer, uinteger, octet_str, object_id, counter,
null (for gauges, use "uinteger"; for bit strings, use "octet_str").
Note that setting an object to "null" effectively delete's it as being
accessible.  No VALUE needs to be given if the object type is null.
.IP
More types should be available in the future.
.PP
If you're trying to figure out aspects of the various mib modules
(possibly some that you've added yourself), the following may help you
spit out some useful debugging information.  First off, please read
the snmpd manual page on the -D flag.  Then the following
configuration snmpd.conf token, combined with the -D flag, can produce
useful output:
.IP "injectHandler HANDLER modulename [beforeThis]"
This will insert new handlers into the section of the mib tree
referenced by "modulename".  If "beforeThis" is specified then the
module will be injected before the named module.  This is useful for
getting a handler into the exact right position in the chain.
.IP
The types of handlers available for insertion are:
.RS
.IP stash_cache
Caches information returned from the lower level.  This
greatly help the performance of the agent, at the cost
of caching the data such that its no longer "live" for
30 seconds (in this future, this will be configurable).
Note that this means snmpd will use more memory as well
while the information is cached.  Currently this only
works for handlers registered using the table_iterator
support, which is only a few mib tables.  To use it,
you need to make sure to install it before the
table_iterator point in the chain, so to do this:

  \fCinjectHandler stash_cache NAME table_iterator\fR

If you want a table to play with, try walking the
\fCnsModuleTable\fR with and without this injected.

.IP debug
Prints out lots of debugging information when
the -Dhelper:debug flag is passed to the snmpd
application.

.IP read_only
Forces turning off write support for the given module.

.IP serialize
If a module is failing to handle multiple requests
properly (using the new 5.0 module API), this will force
the module to only receive one request at a time.

.IP bulk_to_next
If a module registers to handle getbulk support, but
for some reason is failing to implement it properly,
this module will convert all getbulk requests to
getnext requests before the final module receives it.
.RE
.IP "dontLogTCPWrappersConnects"
If the \fBsnmpd\fR was compiled with TCP Wrapper support, it
logs every connection made to the agent. This setting disables
the log messages for accepted connections. Denied connections will
still be logged.
.IP "Figuring out module names"
To figure out which modules you can inject things into,
run \fBsnmpwalk\fR on the \fCnsModuleTable\fR which will give
a list of all named modules registered within the agent.
.SS Internal Data tables
.IP "table NAME"
.\" XXX: To Document
.IP "add_row NAME INDEX(ES) VALUE(S)"
.\" XXX: To Document
.SH NOTES
.IP o
The Net-SNMP agent can be instructed to re-read the various configuration files,
either via an \fBsnmpset\fR assignment of integer(1) to
\fCUCD-SNMP-MIB::versionUpdateConfig.0\fR (.1.3.6.1.4.1.2021.100.11.0),
or by sending a \fBkill -HUP\fR signal to the agent process.
.IP o
All directives listed with a value of "yes" actually accept a range
of boolean values.  These will accept any of \fI1\fR, \fIyes\fR or
\fItrue\fR to enable the corresponding behaviour, 
or any of \fI0\fR, \fIno\fR or \fIfalse\fR to disable it.
The default in each case is for the feature to be turned off, so these
directives are typically only used to enable the appropriate behaviour.
.SH "EXAMPLE CONFIGURATION FILE"
See the EXAMPLE.CONF file in the top level source directory for a more
detailed example of how the above information is used in real
examples.
.SH "FILES"
SYSCONFDIR/snmp/snmpd.conf
.SH "SEE ALSO"
snmpconf(1), snmpusm(1), snmp.conf(5), snmp_config(5), snmpd(8), EXAMPLE.conf, read_config(3).
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